Surgical instruments have been designed in order to provide minimally invasive visual and physical access to certain areas within the human head, such as the suprasellar, parasellar and cavernous sinus areas. With the introduction of rhinoscopy in the mid-19th century, a variety of specula were designed for transnasal surgery. An early speculum designed by Fraenkel combining fenestrated blades with a self-retaining screw arrangement was employed for the first transseptal modification of the transnasal pituitary operation. The fenestrated blades permit a surgical instrument, such as a cutting device, to be inserted through the speculum in order to make incisions into the sphenoidal sinus for instance. In 1914, Cushing designed a speculum whose dimensions allowed improved visualization of the sella floor using a sublabial approach. Later, when the use of surgical microscopes became prevalent, Hardy solved the problem of the speculum's tendency to slip backward by adding toothed edges to the inferior blade surface. A 1975 technical note authored by Landolt and Novoselac, describes a modification to the Cushing speculum in which the distal ends of a speculums blades are bent outward to retain the tissue outside the surgical field. In 1980, Laws and Kern developed a modification of the Hubbard speculum that included a self-retaining retractor and distally flanged concave blades which both frees the surgeon's hands and enhances lateral exposure in the area of interest. More recently, additional modifications to transsphenoidal speculums have been introduced to laterally expand visualization within the sellar area. These changes include thinning the proximal ends of the speculum blades, shortening of one speculum blade for better contralateral exposure and adding an additional hinge to provide a wider surgical field.
Currently available endonasal speculums typically have elongated blades that are curved in cross section from their proximal to distal ends which result in an oval-shaped surgical corridor. Although, the current speculum blade design provides adequate exposure for sellar targets situated directly in-line with the speculum, in many instances the target extends beyond the sellar region either superiorly in the suprasellar space or inferiorly in the clival region. In the event that the target extends beyond the sellar region, inadequate exposure is often encountered if one is trying to access suprasellar tumors such as craniopharyngiomas, tuberculum sella meningiomas or adenomas with large suprasellar extensions. Similarly, access to infrasellar lesions such as clival chordomas or prepontine epidermoid tumors are limited by the curved speculum blade construction. The long tubular construct of the speculum, which is typically 70 to 90 mm in length, further restricts parasellar visualization, which becomes more problematic as the speculum length increases.